Physical Sciences Division Research Highlights

November 2011

An About-Face on Electrical Conductivity at the Interface

Study offers new explanation of conduction at interface of oxide materials

A cross-sectional scanning transmission electron micrograph of the interface between the polar lanthanum chromium oxide (LaCrO3) and the nonpolar strontium titanium oxide (SrTiO3). Although the interface appears to be atomically abrupt, detailed spectroscopic measurements show that cation mixing occurs in the interfacial region.

To improve the electronic devices that keep our modern, hyper-connected world organized, scientists are on the hunt for new semiconductor materials, which control the flow of electricity that powers smart phones and other electronic devices.

One answer could lie with an unusual form of electrical conductivity that takes place at the junction of two oxides, materials made of oxygen and metal. When an oxide made up of alternating positively and negatively charged layers — called polar — is placed in direct contact with a nonpolar oxide, the interface between the two can conduct electricity in a way that could make some novel electronic devices possible.

But a group of scientists were recently surprised to find the interface of two particular complex oxides – the polar lanthanum chromium oxide, LaCrO3, and the nonpolar strontium titanium oxide, SrTiO3 – did not conduct electricity.

The scientists – from Pacific Northwest National Laboratory and the University College London in Britain – give a possible explanation for this unexpected result in a paper published in the Nov. 11 issue of Physical Review Letters. Their hypothesis challenges the reasoning that many use to explain conductivity at the interface of complex oxides.

"To create the next generation of electronic technologies that society needs to progress, a replacement for silicon will be needed," said PNNL Laboratory Fellow Scott Chambers, the paper's lead author. "Our research sheds light on why conduction may or may not occur in one candidate, complex oxides."

Funding: This work was supported by DOE's Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and Chemical Sciences, Geosciences, and Biosciences Division and the Royal Society

User Facility: The experimental work for this research was conducted in the oxide epitaxy lab that Chambers oversees at EMSL